Abstract:

The invention relates to an inexpensively-/easily-decommissionable nuclear
power plant, where a nuclear isle of one or more nuclear power-stations
is installed in caverns, and further, side by side with them, a centre
for characterising, treating and conditioning radioactive wastes and two
repositories are installed in suitable caverns, with a final repository
being adapted to store low-intermediate level nuclear wastes and a
temporary repository being adapted to store spent fuel, high-level
long-life radioactive materials and, in case, spare nuclear rods for
reactor refueling.

Claims:

1. An underground nuclear power plant, characterised in that a nuclear
isle of one or more thermo-nuclear reactors are installed in caverns, and
further, side by side with them, a centre for characterising, treating
and conditioning radioactive wastes and two repositories are installed in
suitable caverns, with a final repository being adapted to store
low-intermediate level nuclear wastes and a temporary repository being
adapted to store spent fuel, high-level long-life radioactive materials
and, in case, spare nuclear rods for reactor refueling.

2. The underground nuclear power plant according to claim 1, characterised
in that a facilitated decommissioning occurs at the end of the service
life of the nuclear power plant by sealing radioactive components of the
nuclear isle (after closing mechanical openings, disconnecting
commands/control systems and after removing nuclear fuel, liquid of
primary circuit, and, if necessary, those plant parts that are
contaminated by high activity radionuclides), by filling up with
concrete, also of a lightened type, voids of the cavern hosting the
reactor and steam generators, and by closing the entrance of the cavern
with metallic doors of adequate thickness and any interposition of walls
made of injected concrete between said doors.

3. The underground nuclear power plant according to claim 1, characterised
in that an entrance to underground facilities works is made absolutely
secure from both terrestrial terrorist attacks and other attacks
performed by rockets, aircraft and similar weapons.

4. The underground nuclear power plant according to claim 1, characterised
in that the entrance is made so that the underground facilities works
cannot be flooded by extreme natural events.

5. The underground nuclear power plant according to claim 1, characterised
in that the radiation containment systems and the safeguard buildings
protection are realised by the rocks of the caverns appositely modelled
during the excavation in order to host said components.

6. The underground nuclear power plant according to claim 1, characterised
in that any kind of radioactive wastes of low-intermediate level produced
during the service life of the nuclear power plant is stored in a final
way inside the underground plant in safe conditions, and
reducing/avoiding the transport of such wastes outside.

7. The underground nuclear power plant according to claim 1, characterised
in that all high level nuclear material is temporarily stored in the same
site, and if the site is proved as suitable, it will become a final
repository also for the high level nuclear material.

8. The underground nuclear power plant according to claim 1, characterised
in that nuclear fuel supplies can be constituted, thereby reducing the
total number of transports for the nuclear reactor refueling.

9. The underground nuclear power plant according to claim 1, characterised
in that the occupation of an external area is extremely limited.

10. The underground nuclear power plant according to claim 1,
characterised in that masses of natural water can be used for cooling.

11. The underground nuclear power plant according to claim 1,
characterised in that an access to the nuclear power plant is of
horizontal type.

12. The underground nuclear power plant according to claim 1,
characterised in that a system for characterising, conditioning, and
disposing radioactive wastes is provided.

13. The underground nuclear power plant according to claim 1,
characterised in that commercial, high power PWR reactors are used in
said nuclear power plant.

14. The underground nuclear power plant according to claim 1,
characterised in that the underground caverns housing the nuclear isle
and the underground caverns storing the radioactive wastes and materials
have a roof, an inverted arch and side-walls made impermeable, and will
be provided with systems for collecting natural or accidentally released
fluids.

15. The underground nuclear power plant according to claim 1,
characterised in that if the underground nuclear plant is realised under
a pre-existing conventional nuclear power-station (of superficial type)
to be dismantled, the pre-existing conventional nuclear power-station can
be decommissioned by transferring the radioactive wastes so produced into
underground repositories of the new underground power plant, thereby
avoiding any danger of nuclear pollution to the surrounding environment.

Description:

TECHNICAL FIELD

[0001]The present invention relates to a nuclear power plant having
highest ranked safety features, which can be decommissioned with
certainty, easily and in a very inexpensive way at the end of its service
life.

[0002]More in detail, the invention concerns a plan of a nuclear power
system, with its radioactive components and relevant facilities for the
treatment and disposal of radioactive wastes that are located in a safe
manner altogether underground, being covered by an adequate thickness of
rocks. This plan permits an absolute environment and population
protection together with a safe and easy decommissioning.

BACKGROUND ART

[0003]Conventional power plants for the production of electric energy from
controlled-fission nuclear reactions are today designed and constructed
in such a way that all the main works which said power plants are
comprised of, in particular the nuclear isle, the stream generators, the
turbine/electric generator isle and the safeguard buildings, are located
above the soil surface.

[0004]Safety and security of these power plants that are considered as
very dangerous targets, particularly after the Chernobyl power-plant
disaster and the terrorist attacks to the Twin Towers of New York, are
based on various systems. In particular, their safety is obtained by
using redundant structural solutions (for both plant engineering and
building works), separating circuits for heat exchange and cooling,
constructing with pre-assembling piping, adopting high constructive
standards, protecting and multiplying safeguard buildings and applying
extremely rigorous procedures for the management of plants and personnel.

[0005]However it is evident that such solutions are absolutely inefficient
to protect a nuclear power plant against the most probable attacks, i.e.
a launch of large aircraft filled with fuel or explosive, or even of
rockets, towards the nuclear isle or pools containing spent nuclear fuel.
These are scenarios that have become very realistic in the last years.

[0006]It is evident that events of this kind would generate what military
experts cell "dirty bombs", whose effects, even if not so destroying like
those of a nuclear bomb, would be anyway so dangerous to pollute with
following fall out large areas, up to thousands of square kilometres,
with a result of making these areas inhabitable for centuries.

[0007]Several solutions have been proposed by skilled in the art from the
60's. Even if such solutions were not specifically designed to withstand
extreme terrorist attacks that were not foreseeable in the past, they
aimed to reach high safety levels against accidental releases of
radioactive materials, by locating a nuclear reactor in underground
caverns that were excavated for this purpose.

[0008]However, the proposed solutions do not allow sufficiently
advantageous effects to be achieved so that their adoption can be
suggested, on the one hand for the safety, on the other for the overall
economic cost. A solution for an underground nuclear power plant is
disclosed for example in the patent RU No. 2.273.901.

[0009]The solution proposed by the present invention fits in this context,
which provides an embodiment of a nuclear power plant able to assure:

[0010]a strong reduction of the cost needed for decommissioning the
nuclear power plant by applying innovative procedures, the
decommissioning being certain at the end of its life service;

[0011]an absolute protection of population and environment outside the
nuclear power plant from radioactive releases due to either accidental
causes or any terrorist attacks or catastrophic natural events;

[0012]a final supersafe storage of low-intermediate level radioactive
wastes that are produced during the operation of the nuclear power plant,
by avoiding the handing in the soil surface of such radioactive wastes
towards main treatment/conditioning/disposal centres; [0013]an interim,
insuperably safe storage of spent fuel, of high-level long-life
radioactive materials and, if necessary, of spare rods for refuelling the
nuclear reactor;

[0014]a consequent better relationship with the population, and then a
higher certainty of the initial investments.

DISCLOSURE OF THE INVENTION

[0015]These and other results are obtained according to this invention by:

a) applying techniques known in mining that allow underground caverns
having considerable sizes to be excavated, and assure both the nuclear
isle and safeguard buildings and control buildings of a nuclear power
plant to be housed into said caverns, by exploiting their absolute
capability to prevent radiation and radioactive releases of any kind
toward the external environment due to both plant malfunctions or damages
caused by terrorist attacks, in virtue of underground rocks having
suitable thickness (hundreds of meters);b) constructing specific
facilities for characterising, treating and disposing the radioactive
wastes beneath the surface of the ground;c) adopting suitable procedures
for a facilitated decommissioning of the nuclear isle at the end of the
service life of the nuclear power plant.

[0016]Therefore, a specific object of the present invention is an
underground nuclear power system in which the nuclear isle of one or more
nuclear power plants are installed in caverns, and further, side by side
with them, a centre for characterising, treating and conditioning
radioactive wastes and two repositories are installed in suitable
caverns, with a final repository being adapted to store low-intermediate
level nuclear wastes and a temporary repository being adapted to store
spent fuel, high-level long-life radioactive materials and, in case,
spare nuclear rods for reactor refueling.

[0017]Preferably, according to the invention, a facilitated
decommissioning occurs at the end of the service life of the nuclear
power plant by sealing radioactive components of the nuclear isle (after
closing mechanical openings, disconnecting commands/control systems and
after removing nuclear fuel, liquid of primary circuit, and, if
necessary, those plant parts that are contaminated by high activity
radionuclides), by filling up voids of the cavern hosting the reactor and
steam generators with concrete, also of a lightened type, and by closing
the entrance of the cavern with metallic doors of adequate thickness and
any interposition of walls made of injected concrete between said doors.

[0018]Further, according to the invention, an entrance to underground
facilities works is made absolutely secure from both terrestrial
terrorist attacks and other attacks performed by rockets, aircraft and
similar weapons.

[0019]Furthermore, according to the invention, the entrance is made so
that the underground facilities works cannot be flooded by extreme
natural events.

[0020]Yet, according to the invention, the radiation containment systems
and the safeguard buildings protection are realised by the rocks of the
caverns appositely modelled during the excavation in order to host said
components.

[0021]Moreover, according to the invention, any kind of radioactive wastes
of low-intermediate level produced during the service life of the nuclear
power plant is stored in a final way inside the underground plant in safe
conditions, reducing/avoiding the transport of such wastes outside.

[0022]Moreover, all high level nuclear material is temporarily stored in
the same site, and if the site is proved as suitable, it will become a
final repository also for the high level nuclear material.

[0023]Further according to the invention, nuclear fuel supplies can be
constituted, thereby reducing the total number of transports for the
nuclear power reactor refuelling.

[0024]Moreover, according to the invention, the occupation of an external
area is extremely limited.

[0025]Yet, according to the invention, masses of natural water can be used
for cooling.

[0026]Further, according to the invention, an access to the nuclear power
plant is preferably of sub-horizontal type.

[0027]Further, according to the invention, a system for characterising,
conditioning and disposing radioactive wastes is provided.

[0028]Always according to the invention, commercial, high power PWR
reactors can be hosted in said nuclear power plant.

[0029]Yet, according to the invention, the underground caverns housing the
nuclear isle and the underground caverns storing the radioactive wastes
and materials have a roof, an inverted arch and side-walls made
impermeable, and will be provided with systems for collecting natural or
accidentally released fluids.

[0030]Finally, according to the invention, if the underground nuclear
plant is realised under a pre-existing conventional nuclear power-station
(of superficial type) to be dismantled, the pre-existing conventional
nuclear power-station can be decommissioned by transferring the
radioactive wastes so produced into underground repositories of the new
underground power plant, thereby avoiding any danger of nuclear pollution
to the surrounding environment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]The present invention will be now described by an illustrative and
not limiting way, with particular reference to preferred embodiments
depicted in the figures of the enclosed drawings, in which:

[0032]FIG. 1 shows a diagram of a conventional modern EPR nuclear plant;
and

[0033]FIG. 2 diagrammatically shows an embodiment of a nuclear power plant
according to the invention.

DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

[0034]In FIG. 1 of the enclosed drawings, a layout of a modern EPR nuclear
power plant according to the known technique is shown, which comprises a
reactor building 1, a fuel building 2, safeguard buildings 3, diesel
emergency generator buildings 4, an auxiliary nuclear building 5, a
nuclear waste building 6, and a turbine building 7.

[0035]Turning now to FIG. 2, in a plant according to the invention, all
the radioactive components, the relevant safeguard buildings and the
emergency generators are provided inside underground caverns excavated
for this purpose, having adequate dimensions and depth, and being
connected to the surface by means of equipped access inclines and/or
vertical shafts. Thus all the nuclear components can be confined with
respect to the external world.

[0036]In this manner, the following components of a PWR nuclear
power-plant are situated inside the underground caverns:

[0037]reactor/steam generator/pressurizer unit;

[0038]safeguard buildings;

[0039]control room;

[0040]emergency generators.

[0041]Substantially a very reduced volume of buildings remains outside.

[0042]Further, with the same principle, at marginal costs, it is possible
to construct caverns usable, depending on the necessities and the
situation of a Country, [0043]as a final repository of radioactive
wastes of low-intermediate level, [0044]as a temporary repository of
spent fuel and for storing any spare nuclear fuel; [0045]as a final
repository of high level (and/or long life) radioactive wastes.

[0046]Every underground room will be isolated and equipped with suitable
control systems for maintaining pressure differential needed by the
activities to be performed therein. Air extracted for maintaining said
pressure differential will be treated by suitable filtering systems.

[0047]An optimal diagram is that one shown on the left part in FIG. 2,
with the entrance being made in a hill slope so that steam generator and
turbines can be located at the same level.

[0048]In any case, similar results can be obtained (see right part of FIG.
2), with the reactor being placed at a lower level with respect to the
entrance; in this case mayor adjustments should be made to a secondary
circuit, in particular if the turbines were located at a higher level
than the steam generator.

[0049]This solution could be adopted for all those cases in which a site
hosting an old nuclear power plant to be decommissioned should be re-used
for a new nuclear power plant. In this case, the above solution would
allow the external area "to be cleaned up" from the radioactive materials
by simply moving beneath the surface of the ground, into repository
caverns, the radioactive wastes that are produced by decommissioning the
old external nuclear power plant.

[0050]A comparative analysis, which is made from a new French-German
nuclear power plant (1,600 equivalent MW EPR), shows that moving beneath
the surface of the ground the nuclear isle of a conventional nuclear
power plant according to the solution proposed by the invention, does not
imply additional costs with respect to a conventional nuclear plant fully
constructed superficially. In fact, the excavation cost (cavern and
access tunnels), including material and personnel handling systems is
about 150 million of Euro. The figure is very close to, if not even lower
than, the overall amount requested, in the case of the new EPR, for:

[0051]a reactor basement necessary to contain materials melted by a
hypothetical fusion of a reactor core;

[0052]two (inner and outer) shelters for containing the radiation, both
being 1.3 m thick;

[0053]part of the external safeguard buildings, and in particular of the
necessary civil works, as in the EPR configuration, four safeguard
buildings are located around the reactor in a star-shaped configuration
so to reduce the risk to be altogether destroyed by a mono-directional
aerial incursion.

[0054]Tasks today assigned to these components in a classic EPR would be
very well accomplished super-safely by the rock cover above the
underground caverns where the excavations designed to host the
radioactive parts of the nuclear power plant and the safeguard buildings
according to the present invention should be conducted.

[0055]As far as the facilitated decommissioning of the nuclear isle, it
will be obtained:

i.1) by constructing the roof, the inverted arch base and the side-walls
of the cavern for reactor and steam generator in such a way to make them
impermeable and installing an appropriate system for collecting fluids
(which can be both natural or coming from possible accidental
releases);i.2) by applying (after removing, at the end of the service
life of the nuclear power plant, the spent fuel, the circulation liquid
of the primary circuit and, if necessary, the parts contaminated with
high-activity long-life radionuclides, and after sealing the mechanical
openings and disconnecting the command and operating control systems) a
spritz beton lining (or a universal primer for metal/mortars of cement)
on the components to be sealed;i.3) by installing, in the relevant points
of the cavern and the components of reactor and steam generator, sensors
for monitoring temperature, humidity, and radioactivity;i.4) by filling
up voids of the cavern for reactor and steam generator with concrete
injection (possibly of expanded/lightened type);i.5) by hermetically
closing the entrance to the cavern for reactor and steam generator;i.6)
by continuously monitoring the system by the sensors in i.4).

[0056]The safety against external attacks and natural catastrophic events
will be obtained, as already said, by moving to a place beneath the
surface of the ground the nuclear isle, the security systems and the
emergency generators and, moreover, by:

ii.1) anti-intrusion devices located at the entrance of the underground
nuclear power plant;ii.2) anti-flooding devices;ii.3) moving to a place
beneath the surface of the ground, where possible, also partially, the
building hosting the turbines/electrical generators;ii.4) using, where
possible, natural water masses (sea, river . . . ) for the cooling,
instead of air towers;ii.5) devices for maintaining rooms and caverns
depressurised and for treating/filtering the air so extracted.

[0057]The characterisation-localisation-licensing studies will be
developed with the following progression:

iii.1) initial localisation, according to the existing rules, of a site
for hosting a nuclear power plant, a final low-intermediate level
radioactive waste repository (300 years lasting) and a temporary
repository (50 years lasting) for spent fuel, high level wastes and any
spare rods for reactor refueling;iii.2) studies and tests, to be carried
out during a part of the 50-60 years of service life of the nuclear power
plant, in order to verify the suitability of the temporary underground
cavern to house, in a final manner, high-level long-life nuclear wastes
(for 50,000 years).

[0058]A nuclear power plant so designed can use, with relatively simple
modifications feasible in short time, the reactors already licensed and
now existing in the market, of both small and high power.

[0059]Differing from other similar proposals, the caverns will have, as
much as possible, sub-horizontal access (in hill slopes) in order to
avoid any loss of charge in the circuits and, if realised under the
terrain surface in plain areas, will have systems for connecting the
underground facilities to the surface through inclines and/or service
shaft.

[0060]As far as the economic-financial model of the investment necessary
for constructing a plant of the kind here proposed, the solution
according to the invention offers the opportunity of taking into account
from the beginning the times and costs for the decommissioning. Moreover,
these costs can be assumed as substantially negligible (5-10% less than
the costs of a conventional decommissioning) and the decommissioning will
be performed certainly.

[0061]For a conventional, superficially nuclear power plant, its
decommissioning strongly depends on the availability of a radioactive
waste repository, on the necessity of completely dismantling the nuclear
power plant and returning the hosting area to green field condition, on
the distance between the nuclear power plant and the radioactive waste
repository, and, above all, on the uncertainty of the times required for
obtaining the relevant construction authorisation. All these factors make
a correct a priori evaluation of the costs highly improbable.

[0062]Other relevant savings are offered by the possibility of using at
marginal costs, during the construction of the nuclear power plant and
the management of the nuclear waste and/or radioactive material
repositories, the same handling systems to connect the cavern with
outside, that are already arranged for the nuclear isle.

[0063]Therefore, the solution here proposed according to the invention
permits the realisation of a supersafe and easily-/certainly
decommissionable nuclear power plant, so that the recourse of the nuclear
energy is made again acceptable by populations, from the proposal of
installing nuclear reactors beneath the surface of the ground, as already
proposed in the years 60-70.

[0064]The plant according to the invention provides the installation of
the nuclear isle of one or more nuclear reactors in caverns, and further
the installation, side by side with them, of a centre for characterising,
treating and conditioning radioactive wastes and two repositories in
suitable caverns (of which a final one is for low-intermediate level
nuclear wastes and a temporary one is for the spent fuel and high-level
long-life radioactive materials).

[0065]In particular, this allows an extremely simplified decommissioning
immediately at the end of the service life of the nuclear power plant and
the realisation of inviolable accesses to the underground facilities.

[0066]In this manner:

(i) the costs of decommissioning of the nuclear power plants (usually
between 30 and 60% of the cost of construction) are drastically
reduced;(ii) both the decommissioning at the end of the service life of
the nuclear power plant and the final disposal of the low-intermediate
level wastes become certain;(iii) the number of fuel transports for
refueling the reactor is reduced;(iv) the handling of the radioactive
wastes on the soil surface towards the
characterisation-treatment-conditioning-disposal centres is avoided and,
above all, the incomparable capacity of natural protection offered by the
rocks and the possibility of making inviolable accesses to the
underground works can be exploited;(v) nuclear releases towards the
external environment, due to both malfunctions of the plants or leakage
caused by (aerial or terrestrial) terrorist attacks or catastrophic
natural events, are completely avoided;(vi) additional costs are avoided,
the costs for excavations and works for transferring underground the
nuclear isle being compensated by the saving obtained since external
protection works should not be constructed (shelters, sacrificial
basements, redundancies necessary for the physical protection and for the
plural safeguards buildings, minor soil occupation . . . ),(vii) there
are other savings because the characterisation-treatment-conditioning
centre and the two radioactive material repositories can be constructed
at marginal costs, since they could use the handling systems with outside
and the systems for physical protection already implemented for the
nuclear power plant in cavern,(viii) the nuclear power plant can be
constructed with extreme simplicity because it is possible to take
advantage from the high level of technology reached in mining, so that
the components of the main allowable nuclear power plants (from the
French-German EPR to the Westinghouse and Russian WER power plant) can
find (with marginal modifications) an easy arrangement in caverns of
adequate dimensions; modifications that, consequently, can be put into
effect in very short times especially if compared to those required from
other plans of new generation nuclear reactors that are developed at the
moment,(ix) it is possible, during the service life of a nuclear power
plant according to the present patent application (that would demand a
surveying similar to that necessary for localisation of a final
low-intermediate radioactive waste repository in order to be authorised),
to have all the time to carry out procedures able to verify any
suitability of the site to host finally, and not only, also high-level
long-life radioactive wastes. However, such radioactive wastes would be
hosted for 50-60 years in the best manners and in safety conditions, that
are obviously higher than those offered by a conventional nuclear power
plant, which is constructed on the surface.

[0067]The present invention has been described in an illustrative and not
limiting way, according to its preferred embodiments. It should be
understood that variations and/or modifications could be made by skilled
in the art without departing from the scope of the invention as defined
in the enclosed claims.